Field of the Invention
The present invention relates to devices and methods for performing assays to determine the presence or quantity of a specific analyte of interest in a fluid sample.
Description of the Prior Art
Many devices for the detection and/or quantification of an analyte of interest in a fluid sample are well known and are the lateral-flow type or micro-well type. Generally, lateral flow devices include a solid phase fluid permeable flow path through which a sample and various reagents travel by capillary action. The flow path has immobilized thereon various binding reagents for the analyte (or analog thereof), other binding partners, or conjugates involving binding partners for the analyte and members of signal producing systems (e.g., a label). The various assay formats used with these devices are well known for the direct or indirect detection of the analyte of interest in the test sample.m
U.S. Pat. Nos. 5,726,010, 5,726,013, 5,750,333 and 7,816,122, each of which issued to Scott M. Clark and which are assigned of record to IDEXX Laboratories, Inc., the disclosures of which are incorporated herein by reference, describe assay methods and devices that use the formation of a solid phase bound tertiary complex to detect an analyte of interest in a fluid sample. The devices disclosed in the Clark patents utilize a reversible flow in a chromatographic binding assay. An analyte-containing solution is applied to the device and then is transported by capillary action, first in one direction and then in the opposite direction, along an elongated flow matrix. The flow matrix generally includes four different regions. Region one is where a solution having the sample mixed with either a labeled antibody or antigen is added. Region two, also called the detection zone, contains the second antibody or antigen, which is immobilized to a solid phase. Region three contains a site to apply a wash solution. Region four contains an absorbent reservoir located near region one and makes the flow go in the opposite direction. The device also includes means to detect the presence or quantity of an analyte.
The reversible lateral flow device disclosed in the Clark patents works quite well in detecting an analyte in a fluid sample. However, it, like other lateral flow devices, requires relatively significant sample volume and other reagents so that the matrix can be sufficiently wetted to allow for lateral flow of the sample liquid, wash and substrate. More specifically, such lateral flow devices may require approximately 0.35 grams (0.35 milliliters) of the sample liquid. Thus, samples often need to be diluted when sample volumes are small.
Dry chemical reagent test slides having a film surrounded by a frame are also well known in the art and are used to analyze a blood or fluid sample deposited thereon in a chemical analyzer, such as disclosed in U.S. Pat. No. 5,089,229 (Heidt, et al.) and U.S. Patent Application Publication No. 2010/0254854 (Rich, et al.), the disclosures of which are incorporated herein by reference. The sample deposited on the slides reacts with the chemical reagent on the film, and the reflectance or fluorescence of the slides is then measured by the chemical analyzer to detect a compound or substance found in the sample, such as calcium (Ca), aspartate transaminase (AST) or glucose (Glu), which could be an indication of a condition or disease. Only small aliquots of sample fluid need be deposited on the slides for detection of certain indicators of diseases. It would be advantageous if immunoassays could be performed on such dry chemistry analytical instruments using test slides.